In the early 1970's Motor Wheel Corporation of Lansing, Mich. assignee of applicant herein, as well as its then parent, The Goodyear Tire & Rubber Company of Akron, Ohio, developed and introduced to the automotive market an improved form of composite metal-elastomer styled wheel sold under the registered trademark "POLYCAST". Such styled wheels provided an automotive-type wheel in which metallic disc and rim parts of simple, conventional "plain Jane" configuration, for which manufacturing equipment was already available, are utilized as the basic structural "backbone" components to thereby obtain a high strength standardized wheel construction at minimum cost. The aesthetically pleasing appearance was imparted to this standard steel backbone by a permanently adhered ornamental plastic body, either molded separately or in-situ as a homogeneous one-piece body, or in the form of a preformed plastic cover secured by an adhesive foam body to the outboard side of the wheel. This provided an improved anti-noise characteristic to the wheel and enabled the appearance of the wheel to be readily and economically varied to suit different customer's styling requirements without varying the basic structural components of the wheel. Additional benefits resided in the side impact cushioning to prevent damage to the wheel while retaining the high strength and impact resistance advantages of the time-proven conventional ductile steel wheel components. Wider variation in styling and contour configuration were also obtained than were possible in the previous deep drawn styled all-steel wheels.
Various embodiments of such "POLYCAST" wheels, as well as methods and apparatus for producing the same, are set forth in the following U.S. Pat. Nos. assigned to the assignee herein, which are incorporated herein by reference:
______________________________________ 3,669,501 6/1972 Derleth 3,756,658 9/1973 Adams 3,762,677 10/1973 Adams 3,794,529 2/1974 Thompson 3,815,200 6/1974 Adams 3,918,762 11/1975 Hampshire 3,935,291 1/1976 Jackson 3,956,451 5/1976 Adams 4,017,239 4/1977 O'Connell et al 4,251,476 2/1981 Smith 4,398,770 8/1983 Smith 4,659,148 4/1987 Grill 4,682,820 7/1987 Stalter 4,786,027 11/1988 Stalter 4,790,605 12/1988 Stalter S/N 285,634 F/D 12/1988 Stalter, now U.S. Pat. No. 4,963,083 ______________________________________
Other prior art patents issued to unrelated parties and directed to various types of styled metal and plastic wheels include U.S. Pat. Nos. 3,823,982, 3,827,756, 3,894,775, 3,915,502, and 3,998,494 as well as British Patent No. 1,290,946 (1972) and German Offenlegungschrift 2,457,907 (Jun. 6, 1976).
In one commercial method of manufacture of such POLYCAST wheels, a portion of the mold comprises a conventional metal vehicle wheel having a drop center rim secured to a central disc or body having the usual bolt circle holes and a central aperture so that the disc can be mounted on an axle, drum or disc brake assembly. The metal wheel is employed in conjunction with an inboard back-up clamp and an outboard mold part to define therewith a sealed cavity for molding and attaching a three-dimensional contoured plastic overlay, the overlay thus being molded in situ and permanently attached to the outboard side of the wheel while in the mold apparatus. Preferably, in one commercial embodiment of this method the wheel forms the upper surface of the mold cavity and a reaction mixture of a urethane elastomer liquid adhesive material is injected or poured into the mold to fill the cavity and contact the outboard surface of the wheel assembly. The urethane material solidifies to form a high density non-cellular elastomer body which permanently adheres to the outboard surface of the wheel subassembly. The plastic overlay may also be constructed from a lower density microcellular closed cell urethane elastomer adhesive material. After the urethane material has solidified in the mold cavity, the mold is opened so that the wheel with the overlay securely adhered to it may be removed from the mold. The overlay may then be painted or otherwise covered with a decorative coating to provide a finished metallic-appearing ornamental wheel. The urethane elastomer thus forms a plastic body having a three-dimensional contour which is permanently attached to the outboard side of the wheel to provide a decorative surface, and the elastomer overlay appears to be an integral portion of the metal wheel.
Due to the orientation of the overlay beneath the wheel disc, the outboard face of the overlay is adjacent the lowermost surface of the mold cavity. Hence reaction-generated gas bubbles tend to rise and migrate toward the inboard portion of the overlay closest to the wheel disc while the reaction mixture is still liquid. This migration results in a variation in density axially of the overlay so that a relatively dense skin is produced adjacent the outboard face of the overlay, the urethane becoming less dense and more cellular axially towards the disc. Any molding defects, such as large pockets or bubbles, will tend to occur adjacent or at the interface of the overlay and the disc where, generally speaking, such defects are less critical and do not spoil the end product, as compared to casting the overlay with the lower mold part inverted and superimposed on the rim and disc subassembly, which tends to locate such casting defects at the outboard face of the overlay.
The higher density skin at the outboard face of the overlay is advantageous from the standpoint of receiving a painted finish, or receiving a decorative surface texture or finish cast into the outboard surface of the overlay, as well as achieving a smooth relatively hard surface less susceptible to damage in use. Preferably the outboard face of the overlay should have a Shore A hardness in the range of at least 85 to 100, with the preferred material having a Shore A the hardness of about 90 to 95. Materials having a lower Shore A hardness of 30 to 60 could be used, but difficulties may be experienced in some applications with such materials flexing or distorting from impacts received as when curbing the wheel. Accordingly, the polyurethanes or elastomers employed in the overlay should have an outboard surface hardness at least equivalent to that of a pneumatic tire to be used with the wheel, such being usually a minimum Shore A hardness of at least 60 and preferably about 70 or higher.
When using a slight blowing urethane material to provide a micro-cellular overlay, a wide range of densities may be obtained ranging downwardly to about 30 pounds per cubic foot. Non-rigid urethane elastomer materials are available having much lower densities than 30 pounds, ranging down into the 20 or 10 pound range, but the skins on an overlay cast from such material tend to be relatively porous, and hence difficulty is experienced in obtaining a satisfactory mirror-smooth surface to be painted, if such is the effect desired. However, when simulating a sand cast aluminum surface of certain aluminum sport wheels, a less dense and more cellular urethane overlay is desirable inasmuch as painting the same with a conventional metallic aluminum paint will result in the paint solvents partially etching the surface and opening up the pores. This in turn gives a surface appearance substantially identical to that of sand cast aluminum. Similarly, if a wood grain effect is to be imparted to the outboard face of the overlay, low density highly cellular urethane overlays are advantageous since they lend themselves to etching finish treatments used in bringing out simulated wood grain effects.
On the other hand, the higher density materials are preferred from the standpoint of structural strength needed to maintain the shape of the overlay, particularly where relatively complicated contours are employed in the overlay, such as protruding air scoops and the like which must retain their physical shape and orientation even when subjected to the distortional effects of road shocks and bump impacts, curb scuffing and centrifugal forces exerted at high wheel speeds. For this reason, densities on the order of 50 pounds or more per cubic foot have generally been preferred in constructing the commercial composite decorative POLYCAST wheel constructions. A density of 53 to 54 pounds per cubic foot has proven to be highly satisfactory in producing the aforementioned simulated aluminum sport wheel having an outboard surface painted with metallic aluminum paint and simulating sand cast aluminum, but with relatively deep axially extending air scoops requiring considerable structural strength in the overlay.
From the foregoing it will be understood that the composite POLYCAST wheel constructions provides several advantages. It had long been customary to "dress up" a non-decorative conventional steel wheel by removably affixing a decorative wheel cover to the outboard face of the wheel. However, with the decorative POLYCAST wheel construction no additional wheel cover is needed, and at the same time a safer product is obtained because the non-metallic overlay is permanently affixed to the wheel in a very secure manner. Hence there is no accidental detachment problem, a hazard which is associated with conventional removable wheel covers which can and do on occasion fly off a wheel of a passenger vehicle while traveling at high speed. The mechanical fasteners, clips, etc. associated with wheel covers may also be eliminated. Affixing the elastomer overlay to the wheel disc with a permanent adhesive bond during manufacture of the wheel rather than as a later add-on insures better control of this safety factor. The casting or molding in place of the overlay also insures that the mass of the decorative overlay is positioned in a concentric and arcuate relationship to the wheel disc and rim so that the resulting composite wheel is well balanced, dynamically and statically. Although it is to be understood that POLYCAST wheel constructions include those in which the elastomeric decorative overlay is cast or molded as a separate entity from the rim and disc of the wheel, and then subsequently permanently attached to the outboard face of the wheel rim and/or disc such as by a suitable adhesive, this alternative construction requires additional assembly and fixture apparatus in order to achieve the necessary concentricity and balance tolerances. Hence, the cast-in-place method described previously has been preferred commercially because less production equipment is required and the separate attachment step is eliminated.
Another advantage of composite decorative POLYCAST wheels is the flexibility they provide to both the wheel designer and to the wheel manufacturer. The designer can exercise wider latitude in his choice of shapes and contours since the designer is no longer inhibited by the limitations involved in deep drawing of the metal of the wheel disc in order to achieve an aesthetically pleasing appearance. The wheel manufacturer can economically produce a standard steel wheel rim and disc subassembly for a whole series of different wheel designs, thereby greatly reducing production costs because of this standardization. The extensive capital investment required in drawing equipment is greatly reduced, and design changes can be quickly accomplished with only a minimum of re-tooling of the comparatively inexpensive molding equipment required to cast the non-metallic decorative overlay against the wheel.
Due to the elastomeric nature of the overlay, it provides a further safety feature in that it can serve as a cushion which offers protection to the main structural steel components of the wheel in the event of a side impact, as when the wheel strikes a curb, thereby reducing the exposure of these components to stress risers and cracks. It has also been found that the urethane elastomer will flow during pouring and curing into the minute clearance spaces in the interface between the rim and disc which may remain between the circumferentially spaced spot or arc welds joining the same. This will provide a thin resilient cushion between these steel parts of the wheel which is believed to reduce wheel-generated noise, transmission of noise through the wheel, and corrosion. In recent years the wheel disc peripheral flange has been designed to have a press-fit assembly into the rim well inner peripheral surface. Due to this tight fit, very little air leakage will be obtained via the rim-disc interface during the mold filling operation even though the rim-disc weld joint is circumferentially discontinuous. Hence, with this type of rim-disc subassembly, four equally angularly spaced external air vent grooves are provided in the disc peripheral flange, each measuring about one millimeter in radial depth and about four millimeters wide (circumferentially of the disc flange). This venting of the root of the rim-disc outboard valley space helps insure full filling and penetration of the mold cavity by the liquid urethane reaction mixture, as well as providing the aforementioned cushion and noise reduction effect.
It also is to be understood that the overlay may also cover a portion or all of the outboard face of the wheel rim and be adherently secured thereto in the same manner as it is to the disc. Such additional coverage helps further reduce any transmission of noise through the wheel. In some instances, the overlay may overlie and be secured only to the rim, leaving the entire disc or a portion thereof uncovered and exposed to view.
The inventions of the above-listed "POLYCAST" wheel patents have achieved widespread commercial success: millions of such "POLYCAST" wheels having been successfully made and sold over the past eighteen years in an almost infinite variety of decorative configurations and ornamentation of the plastic outboard face component. Moreover, in view of the foregoing factors, the molded in-situ urethane decorative body improvement as disclosed and claimed in the above-listed Adams '677, '200, '762 and '451 patents have been favored commercially over the particular exemplary embodiments of the POLYCAST wheel invention as first disclosed in the above-listed pioneer Derleth U.S. Pat. No. 3,669,501 and the particular improvement thereon disclosed and claimed in the above-listed Smith U.S. Pat. No. 4,251,476, i.e., a vacuum formed ABS plastic outer cover or a spray-applied outer skin material adhered by a low density urethane foam to the metal components of the wheel. In addition, the density of the urethane employed in the commercial POLYCAST wheels has remained in the 40-50 pounds per cubic foot range despite the obvious weight disadvantage of employing the higher versus lower density urethane materials and/or the particular exemplary light-weight embodiment of the POLYCAST wheel disclosed in the Derleth '501 and Smith '476 patents.
Among various attempts in the prior art to solve the weight reduction problem in composite plastic and steel wheels utilizing a homogeneous decorative body construction, the prior art Kronprinz AG Brinkmann et al German Patent (Offenlegunschrift) 24 57 907 may be noted. This patent discloses a POLYCAST type wheel construction intended to reduce the weight-to-volume ratio of the plastic portion to thus reduce the total weight of the wheel by providing cavities between the wheel disc and the plastic part. In the embodiment of FIG. 1, the plastic part 12 is made as a preform separate from the wheel with cavities 3 in the inner peripheral face of the plastic part 12 to reduce the weight of the same. The preformed plastic part 12 is affixed to the rim 1 at 14 by gluing.
In the embodiment of FIG. 2 the plastic part 12 is formed in-situ by mold foaming the same onto the vehicle wheel by using the cover mold 15 as in the aforementioned Adams Patents. In this process the weight reducing cavities 3 are formed by using film plastic bags 5 filled with a filler material 4 disposed in the mold cavity. Each bag 5 has a film portion 5a which serves as a pull tab extending outside of the mold cavity between the inner peripheral edge of the mold lid 15 and the disc crown 2a. After the mold cavity has been filled with the urethane material to form the plastic portion 12 and the mold cover 15 removed from the wheel, bags 5 are pulled from beneath the plastic part 12 toward the center of the wheel to leave the cavities 3. In order to permit removal of the core bags 5, mold release material is provided on the bags and the wheel disc, and the inner periphery 12a of the plastic part 12 must rest loosely against the wheel disc 12 rather than being adhered to the same. The free parts of the wheel disc 2 which remain between the bags 5 are likewise provided with a separating agent, so that the plastic part 12 can yield sufficiently to enable the bags 5 to pull out from beneath the same.
The resulting bag-cored cavities 3 are thus circumferentially spaced from one another around the plastic part so as to be disposed circumferentially individually between the disc vent holes. Accordingly, the weight reduction obtainable is limited by this relatively expensive approach to the problem. Penetration and coverage of the plastic material to juxtaposed rim and disc outboard faces and joints is also severely comprised and security of attachment is less than desirable. In any event, so far as is known, this approach has not to date been deemed a practical solution to the weight reduction problem.
Other possible solutions might initially appear to reside in prior art patents directed to other aspects of composite metal and plastic wheel constructions. For example, the aforementioned Motor Wheel Grill U.S. Pat. No. 4,659,148 shows in the embodiment of FIGS. 1-9 a POLYCAST wheel construction with retainer 60 secured to the outboard face of the wheel disc and having a wall encircling the disc holes so as to separate the overlay material from the bolt circle area of the disc. The overlay material engulfs the retainer wall and thereby hides some or all of the retainer from view, and assists in securement of the retainer to the disc. The Grill embedded retainer enables the "POLYCAST" wheel to have a "full-face" decorative appearance while keeping the urethane material of the decorative overlay away from the bolt circle region 64 so that the urethane is not damaged by excessive heat generated during braking, which causes high temperatures in the bolt circle region 64. In some embodiments, a "POLYCAST" wheel construction made pursuant to the Grill '148 patent would have some weight savings over a comparable full-face POLYCAST wheel wherein the urethane extended down into the bolt circle region, absent the retainer 60.
The 1975 Connell U.S. Pat. No. 3,915,502 shows a preformed rigid plastic wheel cover 12 adhered to the outer face of the metal wheel disc 30 by a double-coated adhesive tape 40 of circular shape disposed at the crown of the disc. The outer periphery as well as the inboard face of the wheel cover are configured to leave voids or spaces between these cover faces and the juxtaposed faces of the wheel disc and rim. The tape 40 is stated to permanently mount the wheel cover to the wheel disc, and hence, as in POLYCAST wheel constructions, clearance holes are provided in the cover to permit the wheel to be removed from the wheel hub without the need to remove the cover from the wheel. Although no mention is made of reduction in weight from the Connell "taped-on" plastic wheel cover arrangement, the voids between the cover and wheel would inherently perform this function. However, the evident drawbacks of this approach to a POLYCAST wheel undoubtedly explain why the same, so far as is known, has not been commercialized to date.
The 1975 Christoph et al U.S. Pat. No. 3,894,775 provides a disclosure similar to that of the Connell '502 patent in that Christoph et al shows a rigid plastic wheel cover which, in most if not all of the disclosed embodiments is permanently affixed to the wheel and provided with clearance holes or large center opening (FIGS. 15 and 16) for the wheel mounting bolts to permit the wheel to be removed from the axle without the need to remove the cover from the wheel. In the embodiments of FIGS. 1 and 2 the inboard face of the wheel cover is configured to leave voids or spaces between the cover and the juxtaposed outboard faces of the wheel disc and rim. Again, although no mention is made of reduction in weight from the Christoph et al plastic wheel cover arrangement of FIGS. 1 and 2, the voids between the cover and the wheel would inherently perform this function in the same sense as would conventional removable wheel covers. Again, so far as is known, the Christoph et al construction has not been commercialized to date.
The Motor Wheel Weeks U.S. Pat. No. 4,449,756 is of general interest to show in the FIG. 3 embodiment of a military tank wheel a separately formed insert 40, formed of an injection molded elastomeric material in the form of a hollow tubular structure of tough closed-cellular material. In assembly, insert 40 is cut to desired length and then permanently sealingly secured to the wheel 12 with opposing ends in sealing abutment as at 42. The purpose of insert 40 is to fill the mud collecting annular channel pocket formed by the cup-shaped configuration of rim 16 and disc 14 of a military tank or other tracked vehicle wheel. Insert 40 is intended as an alternative embodiment to the molded in-situ urethane bodies of the embodiments of FIGS. 2 and 4. Of course, there is no teaching or suggestion in the Weeks '756 patent that insert 40 could be used in any manner as a weight reducing insert in combination with the urethane bodies of FIGS. 2 and 4, much less in an automotive POLYCAST styled wheel construction.